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Date: Sun, 19 May 2024 11:17:16 -0700
From: Ian Rogers <irogers@...gle.com>
To: Arnaldo Carvalho de Melo <acme@...hat.com>, Namhyung Kim <namhyung@...nel.org>, linux-kernel@...r.kernel.org,
linux-perf-users@...r.kernel.org
Cc: Ian Rogers <irogers@...gle.com>
Subject: [PATCH v1] tools api io: Move filling the io buffer to its own function
In general a read fills 4kb so filling the buffer is a 1 in 4096
operation, move it out of the io__get_char function to avoid some
checking overhead and to better hint the function is good to inline.
For perf's IO intensive internal (non-rigorous) benchmarks there's a
near 8% improvement to kallsyms-parsing with a default build.
Before:
```
$ perf bench internals all
Computing performance of single threaded perf event synthesis by
synthesizing events on the perf process itself:
Average synthesis took: 146.322 usec (+- 0.305 usec)
Average num. events: 61.000 (+- 0.000)
Average time per event 2.399 usec
Average data synthesis took: 145.056 usec (+- 0.155 usec)
Average num. events: 329.000 (+- 0.000)
Average time per event 0.441 usec
Average kallsyms__parse took: 162.313 ms (+- 0.599 ms)
..
Computing performance of sysfs PMU event scan for 100 times
Average core PMU scanning took: 53.720 usec (+- 7.823 usec)
Average PMU scanning took: 375.145 usec (+- 23.974 usec)
```
After:
```
$ perf bench internals all
Computing performance of single threaded perf event synthesis by
synthesizing events on the perf process itself:
Average synthesis took: 127.829 usec (+- 0.079 usec)
Average num. events: 61.000 (+- 0.000)
Average time per event 2.096 usec
Average data synthesis took: 133.652 usec (+- 0.101 usec)
Average num. events: 327.000 (+- 0.000)
Average time per event 0.409 usec
Average kallsyms__parse took: 150.415 ms (+- 0.313 ms)
..
Computing performance of sysfs PMU event scan for 100 times
Average core PMU scanning took: 47.790 usec (+- 1.178 usec)
Average PMU scanning took: 376.945 usec (+- 23.683 usec)
```
Signed-off-by: Ian Rogers <irogers@...gle.com>
---
tools/lib/api/io.h | 69 +++++++++++++++++++++++++---------------------
1 file changed, 38 insertions(+), 31 deletions(-)
diff --git a/tools/lib/api/io.h b/tools/lib/api/io.h
index 84adf8102018..d3eb04d1bc89 100644
--- a/tools/lib/api/io.h
+++ b/tools/lib/api/io.h
@@ -43,48 +43,55 @@ static inline void io__init(struct io *io, int fd,
io->eof = false;
}
-/* Reads one character from the "io" file with similar semantics to fgetc. */
-static inline int io__get_char(struct io *io)
+/* Read from fd filling the buffer. Called when io->data == io->end. */
+static inline int io__fill_buffer(struct io *io)
{
- char *ptr = io->data;
+ ssize_t n;
if (io->eof)
return -1;
- if (ptr == io->end) {
- ssize_t n;
-
- if (io->timeout_ms != 0) {
- struct pollfd pfds[] = {
- {
- .fd = io->fd,
- .events = POLLIN,
- },
- };
-
- n = poll(pfds, 1, io->timeout_ms);
- if (n == 0)
- errno = ETIMEDOUT;
- if (n > 0 && !(pfds[0].revents & POLLIN)) {
- errno = EIO;
- n = -1;
- }
- if (n <= 0) {
- io->eof = true;
- return -1;
- }
+ if (io->timeout_ms != 0) {
+ struct pollfd pfds[] = {
+ {
+ .fd = io->fd,
+ .events = POLLIN,
+ },
+ };
+
+ n = poll(pfds, 1, io->timeout_ms);
+ if (n == 0)
+ errno = ETIMEDOUT;
+ if (n > 0 && !(pfds[0].revents & POLLIN)) {
+ errno = EIO;
+ n = -1;
}
- n = read(io->fd, io->buf, io->buf_len);
-
if (n <= 0) {
io->eof = true;
return -1;
}
- ptr = &io->buf[0];
- io->end = &io->buf[n];
}
- io->data = ptr + 1;
- return *ptr;
+ n = read(io->fd, io->buf, io->buf_len);
+
+ if (n <= 0) {
+ io->eof = true;
+ return -1;
+ }
+ io->data = &io->buf[0];
+ io->end = &io->buf[n];
+ return 0;
+}
+
+/* Reads one character from the "io" file with similar semantics to fgetc. */
+static inline int io__get_char(struct io *io)
+{
+ if (io->data == io->end) {
+ int ret = io__fill_buffer(io);
+
+ if (ret)
+ return ret;
+ }
+ return *io->data++;
}
/* Read a hexadecimal value with no 0x prefix into the out argument hex. If the
--
2.45.0.rc1.225.g2a3ae87e7f-goog
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